Abstract
Air and ground temperatures were monitored on and around blocky deposits such as rock glaciers and talus slopes in the alpine zone of the Yari-Hotaka Mountains, northern Japanese Alps, using miniature temperature data loggers. The results of air temperature monitoring indicated that the mean annual air temperature in the summit area of the Yari-Hotaka Mountains was about −2.5°C, and this area belong to the discontinuous permafrost area.
The results of ground surface temperature at leeward sites (Tenguppara cirque and Oh-kiretto cirque) showed that a sufficiently thick snow cover insulates the ground surface from short-term variations in atmospheric conditions during the winter. At some of these sites, the bottom temperatures of snow cover (BTS) in late winter were less than −3°C, and mean annual ground surface temperatures (MAST) were less than 0°C. These results suggest that mountain permafrost can be present in some blocky deposits. BTS values at significantly large boulder site were distinctly colder than those at other sites. This intensive cooling of the ground surface may be caused by conduction through surface boulders protruding into and through the snow cover.
At some wind-blown sites located on a rock glacier in the northern Minamisawa cirque, ground surface temperatures were influenced by atmospheric variations throughout the whole winter, and MAST was close to 1°C. Ground surface temperature evolution on the furrows of this rock glacier do not undergo short-term fluctuations during the winter, and BTS in late winter at these sites was less than −3°C. These results suggest the occurrence of patchy permafrost in this rock glacier.
